640 GHz SIS RECEIVER SYSTEM FOR JEM/SMILES ON ... · PDF fileWe succeed in demonstrating the cooling capability of 20 mW at the 4-K ... that the basic ozone ... is suitable for keeping

Tenth International Symposium on Space Terahertz Technology, Charlottesville, March 1999

640 GHz SIS RECEIVER SYSTEM FOR JEM/SMILES ONINTERNATIONAL SPACE STATION

M. Seta, H. Masuko, and T. Manabe

Communications Research Laboratory (CRL). Ko ganei. Tokyo 184-8795. Japan

TEL: +81-42-327-5367. FAX: +81-42-327-6110. E-mail: [email protected]

J. Inatani

National Space Development Agency of Japan (NASDA). Tsukuba. Ibaraki 305-8505. Japan

JEM/SMILES mission team

NASDA, CRL

ABSTRACT

We are developing a superconductor-insulator-superconductor (SIS) receiver for a submillimeter-

wave limb emission sounder (SMILES) on the Japanese Experiment Module (JEM) of the

International Space Station. SMILES is a sensitive heterodyne spectrometric radiometer in 640

GHz band, and observe thermal emission lines of stratospheric trace molecules in the limb

sounding method. SMILES operates two SIS mixers simultaneously in sin g le-sideband (SSB)

mode using only one local source. For the SSB filter we employ a frequency selective polarizer

(FSP), which consists of two sets of a wire grid and a flat mirror and operates in the principle of

Martin-Puplett interferometer. The SIS mixers and the first low noise amplifiers will be cooled to

4.5 K and 20 K, respectively, by a compact Stirling refri gerator combined with a Joule-Thomson

circuit. We succeed in demonstrating the cooling capability of 20 mW at the 4-K sta ge. 200 mW at

the 20-K stage, and 1000 mW at the 100-K sta ge with a power consumption of 250 W. We

expect a system nose temperature below 500 K in the SSB mode. In 2003 SMILES will become

the first SIS receiver flown on space.

INTRODUCTION

Stratospheric minor constituents (e.g.. 03, ClOx, N0x) play an important role in the Earth

environmental change such as ozone depletion. Although we know that the basic ozone depletion

process are caused by man-made chemical substances such as chlorofluorocarbons. researches on

the complicated chemical network of the ozone depletion are still in progress. We need data of

global distributions of these minor gases and their diurnal and seasonal variations with a high

altitude resolution. We are now developing a highly sensitive submillimeter-wave limb emission

436


sounder (SMILES) to promote sciences related to the ozone depletion (e.g., Masuko et al. 1997;

Manabe et al.. 1998). SMILES will be installed on the exposed facilities of the Japanese

Experiment Module (JEM) of the International Space Station (15S). In the limb sounding method,

thermal emission from the stratospheric molecules are observed by a sounder on the orbit (e.g.,

Barrath et al.. 1993). Figure 1 shows the schematic drawing of the limb sounding observation by

SMILES. We expect to start a operation of SMILES in 2003 for at least one year, and now we are

in the final design trade-off of the system. This paper mainly describes the current instrumental

desi gn of the 640 GHz SIS receiver system, and also reports some experimental results.

OVERVIEW OF JEM/SMILES

Table 1 summarizes the basic specifications of JEM/SMILES, and Fi gure 2 shows the signal

flow diagram of SMILES. We employ a hi ghly sensitive heterodyne superconductor-insulator-

superconductor (SIS) receiver, and observe twelve emission lines of stratospheric molecules as

listed in Table 2. The SIS receiver makes it possible to detect extremely weak emissions and

reduce the observational time for each observational positions. We retrieve the altitude profile of

the molecules at a high altitude resolution over a wide altitude range together with their global

diurnal and seasonal variations from the sensitive data set.

A 60 cm x 30 cm main reflector gathers the thermal radiation from the atmospheric limb

region at an altitude resolution of 2 km. The 638.4 GHz fixed frequency LO signal is injected into

the RF signal by wire grids. In order to measure the intensity of the si gnal in one sideband

precisely. we use the receiver in single-sideband mode (SSB) by a quasi-optical SSB filter. We

operate two SIS mixers simultaneously. one for upper sideband (USB) and the other for lower

sideband (LSB) detection. The IF signals of 9.8 -14.8 GHz are further down-converted in

frequency and amplified to a power level large enough for spectroscopy. In the IF subsystem only

frequency ran ges around the molecular emission lines of interest are chosen to save the band

width of the spectrometer. We use three acousto-optical spectrometers (AOSs) for high resolution

spectroscopy. The system noise temperature is expected to be less than 500 K in SSB mode,

which g ives a sensitivity of 1.3 K for an integration time of 0.2 sec and a spectral resolution of

1.4 MHz.

SUBMILLIMETER ANTENNA

We require several technical specifications in the antenna of SMILES for demonstrating a

highly sensitive limb emission technique from the space. First requirement is an altitude resolution

of 2 km with precise pointing accuracy of 0.01 We use an offset Casegrain type elliptical (60 cm

x 30 cm ) antenna. The long axis of 60 cm is chosen to realize an altitude resolution of 2 km, and

another axis is reduced to 30 cm for compactness. The main reflector of the antenna will be

polished aluminum. and special attention is paid in the frame structure of the main reflector and

thermal insulation around the antenna for minimizin g the thermal distortion. We drive the pointing

elevation an g le of the antenna in a step size smaller than 0.01'. The altitude pointing of the antenna

437

100 km

60 km

10 km

2000 km JEM, SMILES

AntennaStratosphere Scan

Tangent Height

• 400 km

A;#r-90 km

Earth

Table 2. Observin g. Molecular Species.Species Frequency

(GHz)Brightne ssTemp. (K) Comments

,() 650.733 220

.Ozone Ler.Globa! Warming

0 ! '0 6 2 7.773 80 T and P measurement,CIO 649.45 20 Ozone DepletionHCI 100 Cl ReservoirHOC1 3 Cl ReservoirNO 651.772 8 Ozone DepletionN:0 652.834 30 NOx ReservoirHNO3 650.279 5 NOx Reser\ oirHO: 649.701 5 Ozone DepletionH20.: 627.087 0.3 HOx ReservoirBrO 624.77 0.3 Ozone De.pletionSO: 624.344

,O.") _Aerosol Source


Fig. 1. Schematic view of the limb sounding observation byJEWSMILE.

Table 1. Basic Specifications ofJEM/SMILES

Receiver

,Heterodyne Spectrometric-Radiometer

Observation Scheme Limb Sounding

Observation Platform International Space Station

Orbit Altitude —400 km.5 r inclination

Observable LatitudeObservation AltitudeAltitude Resolution

65°N - 38°Sh = 10 - 60 km._. h = 2 km

Antenna Type

Size & Beam width

Offset Cassegrain60 cm. 0.055°(EI.).30 cm, 0.117° (Az.)

Pointing Accuracy 0.01°(EI.)

Signal Frequency 624 - 629 GHz (LSB)649 - 654 GH7 (USB)

SSB SeparationMethod

Quas- optical SSB filterFSP

LO Source Gunn diode (109.4 GHz)doubler+tripler

MixerOperation Temp.

Low noise Amps.

PCTJ type Nb/A10x/[email protected] [email protected]

Spectrometer

Spectral Resolution

Acousto-OpticalSpectrometer (AOS)1.4 MHz

System Noise Temp. 500 K (SS B)Mission Life Time 1 yearWeight & Power 500 kg. 500 WSize 0.8 x 1 x1.9 mLaunch Date _2003

438

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•

Tenth International Symposium on Space Terahenz Technology, Charlottesville, March 1999

support structure is monitored by a stellar compass installed ver close to the antenna. We ‘k ill be

able to determine the positions of the antenna v. ith an accurac‘.. of 0.01' .

Second requirement is precise intensity calibration. We require a hi gh main beam efficiency of

95 % so that undesirable emission from the sidelobe should be reduced. The shape of the main

reflector is modified to produce the hi gh efficiency main beam. and its surface is polished with an

accuracy better than 10 j.irn to reduce the level of sidelobe. We use a temperature monitored

submillimeter-wave absorber at an ambient temperature for a hot load calibration. but we use the

main antenna itself for cold load calibration by pointin g upward directions. We expect a precise

cold load calibration compared with a system lookin g cold sk■ b), a switching mirror in the beamtransportation system, because effect from the surroundings of the optics is kept same duringoperation. The baseline ripple which appears in the observed spectra due to undesired reflectionwithin the system is also a source for reducing the reliability of calibration. We choose offset typeantenna for avoiding the beam reflection in the antenna which ma:, cause baseline ripple in thespectra. We expect a precise intensity calibration better than 1 0 ck in error.

QUASI-OPTICS

Figure 3 is the schematic drawin g of the receiver optics of SMILES. Optical system is

designed to realize easy ali gnment and reduce the risk of misali gnment caused by variation of

environmental condition on space. The optics are divided into two main components: the optics on

4-K stage and that in ambient temperature. The ambient temperature optics guide the beam from

the antenna subsystem into the cooled optics. The 638.4 GHz LO si gnal is injected into the wire

grid in the ambient optics. Typical physical size of the mirror is ran g in g from 30 mm in the 4-K

stage and 60 mm on the ambient optics. They are settled around the center of cryostat as close as

possible. The center of the cryostat is stable in terms of mechanical structure and thermal

conditions, and concentration of them toward the center is suitable for keeping the good alignment

conditions.

An outstanding feature of the optics is the realization of SSB operation of two SIS mixers

simultaneously using only one local source (Inatani el al.. 1998). Two mixers on the 4-K stage

receive two perpendicular polarizations each other. One mixer looks at the antenna port in the

USB band, while it looks at the cold sky though the LO port in the LSB band. At the same time.

the other mixer looks at the antenna port in the LSB band and the cold sky in the USB band. This

SSB operation is realized by a quasi-optical SSB filter on the ambient temperature optics. The

band suppression ratio of 17 dB is expected at the band edge frequency.

The SSB filter is a key component of the optics. We use a frequency selective polarizer (FSP)

as an SSB filter which use the principle of Martin-Puplett interferometer (MP1) (Seta et al.. 1 999).

The FSP consists of two pairs of a flat mirror and a wire grid. Fi gure 4 shows the operational

principle of the FSP comparing that of traditional MPI consistin g of two roof-top mirrors and a

wire grid shown in Figure 5. The wire grid (WG) #4, whose wire direction is oriented at 45 with

respect to the incident linear polarization. divides the input si g nial into two components. The

reflected and trinsmitted si gnals are combined a gain in WG #5 after traveling two different path

440

LSB SiS Mixer Antenna Port

K ShieldSB StS

FocussjnMirrolV

Wire-Grid #3Cold sky forCold LoadOptics in Ambient

Temperature

Cryostat Wire-Grid #4LO Port

Wire-Grid #1

Fio,cussingrror

Absorber

cus nirrorli

6at Mirror

LO Source

Absorber

4KStage

Roof-Top Mirror MPI

Wire-Grid#1

Flat Mirror

Wire-Grid #4Wire-Grid#5

Flat Mirr-or

FrequencySelectivePolarizer(FSP)


Fig. 3. Schematic view of receiver optics of JEM/SMILES.

#2 Wire-Grid #2

Fig. 4. Schematic drawing of our pro-posed nevi type of SSB filter operatingin the principle of MP!.

Wire-Grid#1

Fig. 5. Schematic drawing of a conven-tional MPI.

441

Tenth International Symposium on Space Temhertz Technology, Charlottesville, March 1999

len gths. We can tune the transmission characteristics in frequenc\ from a imeark polar:zed input

signal to a linearly polarized si gnal in the output port by adjustin g- the tra\ eling path length

difference. The path len g ths is adjusted by a gap between the flat mirror and the w ire g rid. \\ hile

in the conventional MPI the path difference is controlled by the rela:i\ e distance difference

between the WG #4 and each roof top mirror.

The FSP is superior to the traditional MPI in two reasons for our purpose. Since ‘k e use the

SSB filter for a fixed frequency, we do not need tunin g mechanism. A mechanical tuner may be

harmful by increasing possibilities of mechanical troubles in space. So we v, ill use a fixed tuned

SSB filter without movin g mechanical structure. We adjust the position of the mirror in the

ground which works as a tuner, and fix the position ti g htly once it k tuned. The required

alignment accuracy of the mirror is estimated to be 2 um. In the traditional NIPI e must achieve

this accuracy for a traveling path length of 50 mm. and this is too difficult to achie\ e without

mechanical tuning structure. On the other hand in case of FSP. we can adjust the mirror position

in a accuracy of 2 p.m for a path length of 2 mm. which is achieved with careful machine work.

The second advantage of the FSP is elimination of standing waves generated on the MPI. In the

conventional MPI, the input signal partially returns to the input port due to undesirable

transmission and reflection of the wire grid. The returned si gnal becomes a source of standing

wave. This level is estimated to be 20 dB assumin g the undesired reflection and transmission of

the wire grid is 1%, and it is harmful to our sensitive spectroscopic obser\ ation. Althou gh in the

FSP we cannot avoid the undesirable reflection and transmission of the wire grid. this component

never comes back to the input port.

The LO signal at 638.4 GHz is generated in a phase-locked Gunn diode oscillator followed by

a doubler and a tripler, and injected into the FSP through the WG #3. The direction of wires in

WG #3 is tilted 10' from the linear polarization plane of the LO source. so that the local power is

injected into the FSP by 3 % , while each mixer, in its image band. looks at the cold sky by 97 %.

The injected LO power is equally supplied into two mixers. The LO output power. which is

expected to be around 200 pW, is sufficient for operation of two 640-GHz SIS mixers.

SUBMILLIMETER SIS MIXERS AND LOW NOISE AMPLIFIERS

The SIS is the ultimate device for sensitive millimeter and submillimeter observations

especially for 100 - 1000 GHz. Up to now only a Schottky barrier diode type mixer is used in the

space (e.g., Barath et al. 1993). SMILES employs the SIS mixer for the first time in the space.

We use simple and stable SIS mixers for increasing reliability of the mission.

We use a parallel-connected-twin-junctions (PCTJ) type SIS mixer composed of 1.25-micron

Scale Nb/A10x/Nb junctions. which are developed at the Nobeyama Radio Observatory (Noguchi

et, al., 1995; Shi et al., 1997; 1998). The mixer with this device achieves a broad-band

performance without a mechanical tuning structure. We place the SIS device in a wave guide type

mixer-mount in a typical size of 20 mm. A corrugated type feed horn is attached to the mount. and

superconducting ma gnets are inte g rated in the mount to suppress the Josephson current. One

model of the mixer covers both USB (649-654 GHz) and LSB (624-629 GHz). which is

442


advantageous in performing space qualification tests such as vibration and radiation. The mixer

block is attached to the rigid 4K-optics directly with screws. An independent battery will be used

for a DC bias of the mixer for stable operation. Our experiment already demonstrated the mixer

noise of Tmix = 60-140 K in DSB in the frequency range of 600-650 GHz (Irimajiri et at.,

1998).

We require broad band and low power consumption low noise amplifiers for IF amplifiers.

SMILES requires a bandwidth of 5 GHz in the 640 GHz band to detect important molecules listed

in Table 2. and the IF amplifiers should be low noise over the frequency band for high sensitivity.

The power consumption of IF amplifiers should be low for using compact refrigerator. We are

developin g a hi gh-electron-mobility transistor (HEMT) amplifier with a bandwidth of 5 GHz. We

expect a noise temperature below 25 K and a gain of 20 dB with a power dissipation of 20 rnW at

the operational temperature of 20 K. We succeed in demonstratin g this performance in the

engineering model of the HEMT amplifiers.

CRYOSTAT AND MECHANICAL REFRIGERATOR

The SIS mixer needs to be operated below 4.5 K. We chose mechanical refrigerator as a

cooling system. The mechanical refrigerator is superior to liquid helium type cooler for space use

mainly for two reasons. even though it needs la ger electric power. First it can be made smaller and

lighter. because we do not need large helium tank. Second there is possibilities to expand the life

ti me keepin g its smallness and lightness.

We have been developing a compact and low power consumption type refrigerator for space

use. Inatani et al. (1997) reported the experimental results of thermal prototype of the refrigerator,

and concluded that an SIS receiver cooled by a compact 4-K mechanical refrigerator is feasible for

space use. Based on this successful experiment we are developing an advanced type of a compact

refri gerator sy stem for JEM/SMILES. which satisfies the launchin g condition of SMILES. Figure

6 show s the schematic view of our cryostat. In the cryostat. we place two SIS mixers, two HEMT

amplifier.. other two HEMT amplifiers on the 4-K. 20-K. and 100-K sta ges, respectively. The

cryostat is equipped with a Joule-Thomson circuit and a two-stage Stirling refri gerator (Kyoya et

al.. l994. Table 3 shows the thermal anal y sis of the cryostat. The 4-K stage is surrounded with

radiation Nhieids at 20 K and 100 K. and the effect of thermal radiation is minimized with a set of

carefully installed multi-layer insulators. For reducin g the thermal radiation through an RF signal

window . we place two IR filers made of porous polytetrafluoroethylene (PTFE) between the 100-

K sta ge and the outer shell. The coolin g capacity is desi gned to be 20 mW at the 4-K stage, 200

mW at the 20-K sta ge. and 1000 mW at the 100-K sta ge with an electric power consumption less

than 250 W at the AC pow er supply to the refri gerator system.

Mechanically the three sta ges are supported by a number of g lass-fiber reinforced plastics

-(GFRP) straps from the outer shell of the crvostat. The 4-K and 20-K stages are connected by

pole, -.7adeor carbon-I:her-reinforced plastic (CFR!) ) and 20-K and 100-K stage is connected by

poles of GFRP. The GFRP nd CFRP keep the thermal conductance as small as possible while

isur\ the \IN-,1:in, en\ ir)-Inent durin g the la:mch. M\ Lir film is used for outer shell window

443

20K stage

HEMTAmp.

100K stageGFRPstraps

ML1 IR filters

100K shield

20K shield

J-T valve4K stage

Joule-Thomsoncompressor

Two stage Stirlingcompressor

Stirlingcold head

Window

SISmixer


Fig. 6. Schematic view of a small Joule-Thomson circuitcombined with two stage String refrigerator.

Table 3. Calculated thermal balance of 640 GHz receiver for SMILES

Items TypesHeat load at each stage (mW)

100-K stage 20-K stage , 4-K stage,RF input window radiation 150 3 2.4Wall (with MLI) radiation 370 19 0.1Supporting structure conduction 230 47 2.4IF cables condition 90 42 13DC bias cables conduction 28 5 0.6Bias current heat source 9 3 1Monitor cables conduction 11 4 0.6HEMT amps heat source 30 20 -J-T gas cooling heat source 170 87 -Total load (mW) 970 210 20

Equilibrium temperature (K) 99 22 4.5

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to keep the vacuum of cryostat during testing of the receiver on the ground.

By using the engineering model of our cryostat we succeeded in demonstrating the cooling

capability and also demonstrated that the vibration expected during the launch did not change the

capability. The detail of the refrigerator will be given elsewhere (Narasaki et al., in preparation).

IF SUBSYSTEM AND SPECTROMETER

In retrieving altitude profiles from the spectral data, frequency resolution restricts the altitude

resolution in the profile. and the frequency bandwidth restricts the lower altitude limit of the

profile. We employ AOS for getting high spectral resolution and wide bandwidth. AOS is

superior in terms of weight, size, and power consumption compared with other frequently used

digital or filter-bank type of spectrometers. We use three AOSs and achieve a total bandwidth of

about 4 GHz with a frequency resolution of 1.4 MHz. We convert a readout data of the CCD in

the AOS into a 16 bit di gital data every 10 msec. and we integrate it for 200 msec.

In order to save the bandwidth of the spectrometer. only limited frequency ranges of

molecular lines of interest are chosen from the broad band width of 5 GHz, and band-pass-filtered

into sub bands. The divided band is again combined into three AOS input ports for spectroscopy.

We realize observational bandwidth of 800 MHz for 03 using this technique.

CONCLUDING REMARKS

In this paper we reported the basic design of the 640 GHz submillimeter receiver system of

the JEM/SMILES mission. and also reported some experimental results of the engineering model.

SMILES emplo■s a sensitive 640 GHz SIS receiver. We operate two SIS mixers simultaneouslyin the SSB mode. We use a frequency selective polarizer (FSP) as an SSB filter. The STS mixerwill be cooled 4 K b■. a compact Joule-Thomson circuit combined with two stage Stringrefrigerator. In the engineering model of the refrigerator. we demonstrated the cooling capabilityof 20 mW at the 4-K stage. 200 mW at the 20-K stage and 1000 mW at the 100-K Stage. We usethree AOSs for spectrometer. and achieve a frequency resolution of 1.4 MHz and total bandwidthof 4 GHz. We expect a system noise temperature of 500 K in the SSB mode.

We are now making a final design trade-off for JEWSMILES. and the specifications

described here may be subject to minor chan ges. In 2003. SMILES will be transported to BS by

a Japanese transporter vehicle HTV launched by the H-IIA rocket. The SMILES will observe

twelYe stratospheric molecules and reveal interesting phenomena relating to the ozone chemistry.

This mission ‘k ill also demonstrate the feasibilit y- and effectiveness of the SIS receiver as a

sensi:ive s stem for monitorin g_ trace gases in the stratosphere. The success of this new technique

will open new possibilities of submillimeter wave observation in earth science and in astronomy.

ACKNOWLEDGEMENT

We-,tcknow Nlitsu _sn; Electric Comoration for sY stem design of JEM/SMILES. Sumitomo

445


Heavy Industries, Ltd. for development of the refri gerator. Nihon Tsushinki Co. Lzd. for

development of HEMT amplifiers. Paris-Meudon Obser‘ ator■ for desi g n of AOS. Thomas

Keating Ltd. for design of optics. Radiometer Ph y sics GmbH for desi gn of LO stem. and space

instrumentation group of Technical Universit y of Denmark for design of stellar c:ompass. Indeveloping SIS junctions we are collaboratin g with Nobevama Radio ObserN ator INR0‘. We

thank Dr. S.-C. Shi and Dr. T. No p.r.uchi of NRO for technical support and discussions.

REFERENCES

F. T. Barath et al.. The Upper Atmosphere Research Satellite Microwave Limb Sounder

Instrument, J. Geophys. Res., 98, D6. 10751, 1993.

J. Inatani et al., A Submillemeter SIS Receiver Cooled by a Compact Stirrin g-JT Refrigerator.

Eighth Int. Symp. on Space Terahertz Tech.. Harvard Univ.. March. 1997.

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T. No guchi, 5.-C.. Shi, and J. Inatani, An SIS Mixer Usin g Two Junctions Connected in

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with Distributed Junctions Arrays. Ei ghth Int. Symp. on Space Terahertz Tech.. Harvard

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Documents

640 GHz SIS RECEIVER SYSTEM FOR JEM/SMILES ON ... · PDF fileWe succeed in demonstrating the cooling capability of 20 mW at the 4-K ... that the basic ozone ... is suitable for keeping